The present invention relates to a ceramic electronic component comprising dielectric layers formed from a sintered body of ceramic particles and having through holes and via conductors embedded in the through holes of the dielectric layers, and a method for manufacturing the ceramic electronic component.
Recently, ceramic electronic components, especially those comprising two or more dielectric layers stacked one on another such as laminated ceramic capacitor, are increasingly made in such a structure that wiring conductors provided inside of the laminated structure (between the layers) are electrically connected with via conductors that penetrate the ceramic electronic component in the direction perpendicular to the layers, in order to decrease the equivalent series resistance and equivalent series inductance of the wiring conductors.
FIG. 9 is a sectional view showing an example of laminated ceramic capacitor 101 that employs the structure described above. Referring to FIG. 9 the laminated ceramic capacitor 101 in this example has a dielectric block 103 formed by stacking a plurality of dielectric layers 102 made of ceramics.
Provided between the dielectric layers 102 that constitute the dielectric block 103 are internal electrodes 104 and 105 disposed in plurality alternately as the wiring conductors. The dielectric block 103 has via conductors 108 and 109 formed therein so as to penetrate the dielectric block 103 from the top surface 106 to the bottom surface 107 thereof in the direction perpendicular to the stacked layers, while an external electrode 110 that is electrically connected to the via conductor 108 and an external electrode 111 that is electrically connected to the via conductor 109 are formed on the top surface 106 and the bottom surface 107 of the dielectric block 103, respectively.
The internal electrodes 104 are provided on the upper surfaces of the dielectric layers 102 that are disposed as even-numbered layers counting from the top surface 106 of the dielectric block 103, and the via conductor 109 is electrically connected while providing an area 112 that has no electrode formed around the via conductor 108 so as to prevent the electrodes 104 from touching the via conductor 108.
The internal electrodes 105 are provided on the upper surfaces of the dielectric layers 102 that are disposed as odd-numbered layers (except for the top layer, namely the first dielectric layer 102) counting from the top surface 106 of the dielectric block 103, and the via conductor 108 is electrically connected while providing an area 113 that has no electrode formed around the via conductor 109 so as to prevent the electrodes 105 from touching the via conductor 109.
The internal electrodes 104 that are electrically connected to the external electrode 111 through the via conductor 109 and the internal electrodes 105 that are electrically connected to the external electrode 110 through the via conductor 108 are disposed opposite to each other with the dielectric layer 102 therebetween in an area X1 shown in the figure, so as to form a circuit that equivalently functions as a capacitor.
The dielectric block 103 is formed by stacking ceramic green sheets containing ceramic particles and an organic binder resin, of which the dielectric layers 102 are made by the same number as the number of the dielectric layers 102, and firing the stack. The internal electrodes 104 and 105 are formed by applying an electrically conductive paste for wiring conductor that contains Ni powder and the like as an electrically conductive component and an organic binder resin, by screen printing or the like in a predetermined planar configuration on the surfaces of the ceramic green sheets prior to stacking, and firing together with the stacked ceramic green sheets.
The via conductors 108 and 109 are formed, for example, by filling the through holes formed in the stacked ceramic green sheets with an electrically conductive paste for via conductor and firing together with the ceramic green sheets. The electrically conductive paste for via conductor may be an electrically conductive paste for via conductor that contains Ni powder, Cu powder and an organic binder resin, or an electrically conductive paste for via conductor that contains an Ni—Cu alloy powder instead of the Cu powder and the Ni powder, as described in Japanese Unexamined Patent Publication No. 2003-123534.
In these electrically conductive pastes for via conductors, Cu is considered to form solid solution with Ni when fired, so as to achieve satisfactory electrical connection of the via conductors 108 and 109 and the internal electrodes 104 and 105.
However, since the ceramic green sheets and the electrically conductive paste for via conductor show different shrinkage behaviors, namely different values of shrinking rate and amount of shrinkage when fired, and sintering of metal powders contained in the electrically conductive paste for via conductor starts in an early stage at a temperature lower than the sintering starting temperature of the ceramic particles in the ceramic green sheets when fired, voids G1 tend to be formed in the interface between the dielectric layer 102 and the via conductors 108 and 109 even when Cu is contained in the electrically conductive paste for via conductor. When the voids G1 are formed in the interface, reliability of connection decreases due to problems such as failure of electrically connecting the via conductors 108 and 109 and the internal electrodes 104 and 105.
In order to solve the problem described above, it has been proposed to add a specific amount of the same ceramic particles (hereinafter referred to as “inorganic particles”) as the ceramic particles to be contained in the ceramic green sheet to the electrically conductive paste for via conductor, and thereby shift the sintering starting temperature of the electrically conductive paste for via conductor as a whole to a higher temperature, so that the ceramic green sheet and the electrically conductive paste for via conductor have the same shrinking rate and shrinkage amount (Japanese Unexamined Patent Publication No. 2003-229325).
However, when the electrically conductive paste for via conductor contains more inorganic particles, the via conductors 108 and 109 have higher conductive resistance and/or become more likely to break.
Therefore, the inorganic particles to be contained in the electrically conductive paste for via conductor should be limited to be in small quantity. In this case, however, the effect of shifting the sintering starting temperature of the electrically conductive paste for via conductor to a higher temperature produced by adding the inorganic particles is not exerted sufficiently enough to prevent the voids G1 from appearing on the interface between the dielectric layer 102 and the via conductors 108 and 109 effectively.
That is, with the use of the conventional inorganic particles, unless larger quantity of particles are added, it is difficult to prevent the voids G1 from appearing on the interface between the dielectric layer 102 and the via conductors 108 and 109.